European Patent No. 214 629 discloses a device which basically consists of a fluid pump and a trap. In order to break down concretions in the gallbladder, a predetermined quantity of a solvent is introduced into the gallbladder so as to have a dissolving effect upon the concretions. After a specific reaction time, the solvent, together with the secretion from the organ, which has collected in the gallbladder, is drawn off by means of the partial vacuum generated by the fluid pump, into the trap where the secretion, that is to say, the bile, settles in the lower region of the trap since the solvent and the bile can only disperse with respect to one another. The solvent which is then located above the bile can then be reintroduced into the gallbladder to continue the process of dissolving the concretions. The process of supplying and withdrawing the solvent is repeated until either the concretions have been completely dissolved or they have been flushed out as a result of draining the gallbladder. Since, during litholysis, new bile is constantly being produced, it may sometimes be necessary to empty the trap several times in the course of the therapy.